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TaDAD2, a Negative Regulator of Programmed Cell Death, Is Important for the Interaction Between Wheat and the Stripe Rust Fungus

¹College of Plant Protection and Shaanxi Key Laboratory of Molecular Biology for Agriculture, Northwest A&F University, Yangling, Shaanxi, 712100, P. R. China; ²College of Life Science, Northwest A&F University, Yangling, Shaanxi, 712100, P. R. China; ³Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907, U.S.A.

Defender against cell death (DAD) genes are known to function as negative regulators of cell death in animals. In plants, DAD orthologs are conserved but their role in cell death regulation is not well understood. Here, we report the characterization of the TaDAD2 gene in wheat. The predicted amino acid sequence of TaDAD2 contains typical structural features of DAD proteins, including a signal peptide, three transmembrane regions, and a subunit of oligosaccharyltransferase. Transcripts of TaDAD2 were detected in wheat leaves, culms, roots, florets, and spikelets. The expression level of TaDAD2 was reduced in the initial contact with the stripe rust fungus, subsequently induced and peaked at 18 h postinoculation (hpi), gradually reduced at 24 to 48 hpi, and restored to control level at 72 to 120 hpi. In addition, TaDAD2 exhibited positive transcriptional responses to abiotic stresses after the initial reduction at 1 hpi. Overexpression of TaDAD2 in tobacco leaves inhibited cell death. Furthermore, knocking down TaDAD2 expression by virus-induced gene silencing enhanced the susceptibility of wheat cv. Suwon11 to avirulent race CYR23 and reduced necrotic area at the infection sites. These results indicate that TaDAD2 may function as a suppressor of cell death in the early stages of wheat–stripe rust fungus interaction. However, it is dispensable for or plays an opposite role in hypersensitive response or cell death triggered by an avirulent race of stripe rust fungus at late-infection stages.